Christmas card 2018

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Comments in green were written by me. Comments in blue were not written by me.
@Carmel: It's not meant to check your answers. It only shows up red if the number you enter cannot be split into valid pairs (eg the number has an odd number of digits or one of the pairs of digits is greater than 20).
The script for checking the answers doesn't work properly
Thank you Shawn!
So satisfying!
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Great puzzle problems! Hint on #9: try starting with an analogous problem using smaller numbers (e.g. 3a + 10b). This helped me to see what I had to do more generally.
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@Seth: try solving it for 3a+4b, 3a+5b, 4a+5b, etc and look for patterns
Loved these puzzles! I have no idea how to approach #9, though. Will the solutions be posted at any point? Or, can anyone provide a hint to how to approach it?
Blaine said I'd like the puzzle, and he was right, too.
Margaret G
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Great puzzles. Especially enjoyed #9. Thanks for the entertainment!
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Think I got it! A sure sign of spring. number 9 was a struggle.
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Someone told me I would like this puzzle and they were right!
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